Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Gray ME
1102 PM EST Wednesday Dec 17 2014
a weak low pressure system will slowly exit the Gulf of Maine
this evening. By Thursday morning...the low will be over the
Canadian Maritimes and weak high pressure will build in behind it.
There is potential for a weak coastal system Sunday into Monday
that may spread some light snow into the region. Another system
will likely strengthen and pass by to our west during the middle
Near term /until 6 am Thursday morning/...
1100 PM...minor estf update to reflect current mesonet in 1st
730 PM...precipitation was gradually changing to snow and sleet
across the area. I made minor adjustments to 1st period grids to
reflect the current mesonet for this estf update.
elongated area of low pressure in the Gulf of ME at this time...with surface trough
extending back into southern Quebec and Ontario. Overnight upper low
pressure will drift underneath the majority of the County warning forecast area. This should
hold trough back across northern zones...and keep focus of moisture
stream into the western ME mountains and parts of the whites. Hi-res model
forecasts indicate that middle level warmth was likely maximized a
couple hours ago...and we should see a steady cooling trend aloft.
This is confirmed by Plymouth state vertically pointed radar
showing snow levels decreasing over the last hour. Spotter reports
indicate many northern mountains and valleys alike changed over to snow for
good in the last couple of hours as well. Ely upslope flow will
also continue to dynamically cool the column and keep the mountains
snow through the night. Forecast model also deepen the 700 mb low through
midnight...closing off contours as it crosses the state of ME.
This should provide enhanced lift to the northwest of the middle level low
track...again keeping snowfall focused over northern zones. A blend of the
rfc quantitative precipitation forecast and hi-res model guidance was used to provide a
reasonable representation of higher terrain enhancement. Snowfall
will wax and wane a bit this evening as the dry slot lifts through
the area...but I expect forcing to refocus later tonight into Thursday.
Have expanded the winter weather advisories into Coos County New Hampshire...and
all of Oxford...Franklin...and central/southern Somerset in ME. This
will be a relatively long duration light snowfall event...which
complicates things a bit. I could easily see 6+ inches of snowfall
for northern zones...but it may fall in 18 or 24 hours...shy of the 9
inch criteria beyond 12 hours. A heavier band of snowfall this
evening across northern Franklin or Central Somerset could warrant an
upgrade to a warning in those areas.
Short term /6 am Thursday morning through 6 PM Thursday/...
upper low pulls into the Maritimes Thursday...but cool...moist...nwly
flow continues over the region. The forced ascent over the higher
terrain will keep shsn going in the favored northwest upslope regions.
This is likely when the bulk of the accumulations will come for
northern New Hampshire and the White Mountains northwest winds will also be gusty along the
coast and interior.
Long term /Thursday night through Wednesday/...
clearing skies expected Thursday night as low pressure exits into
the Canadian Maritimes. This will be followed by high pressure
building south and into New England from Canada.
Models then bring a weak area of low pressure up the coast Monday
and Tuesday. There is not much consensus with the 12z package with
this feature. Currently the Euro is the furthest west with the
position of the surface and upper level features.
All eyes then shift to the 24th...as low pressure rapidly
intensifies and moves north. Question is whether the system
follows the coastline or crosses over the Great Lakes. For
now...confidence level is low. If the Great Lakes track
verifies...expect locally heavy rain and high winds over the
region. Southeasterly gradient will likely reach storm force for a
short period over the waters with strong gusty winds over land.
Strong winds would likely reach the coastline late Wednesday along
the coast and higher terrain.
Aviation /04z Thursday through Monday/...
short term...areas of IFR conditions will continue to lift northeastward up
the coast this evening...with widespread MVFR lingering in its
wake. Gradually rain showers will mix with and transition to shsn by
Thursday. This will lead to scattered IFR conditions at times near the coast.
In the mountains...IFR conditions will linger through Thursday. Gusty northwest winds
are possible Thursday as well...with gusts at or above 20 kts.
Long term...a few areas of MVFR conditions developing in patchy
light snow Monday night through Tuesday night. IFR conditions
developing with a strong area of low pressure passing by to our
short term...have extended the Small Craft Advisory in time and in area to the
bays...as winds look to increase in northwest flow Thursday. Winds will relax
briefly tonight...but steadily increase by morning as cold air advection
Long term...Small Craft Advisory conditions expected Tuesday...with storm force
winds possible on Wednesday as a strong area of low pressure
brings high southeast winds to the region.
ME...Winter Weather Advisory until 1 PM EST Thursday for mez007>009-
New Hampshire...Winter Weather Advisory until 1 PM EST Thursday for nhz001-002.
Marine...Small Craft Advisory until 4 am EST Friday for anz150>154.